Illuminator, projection display device and method for driving the same

ABSTRACT

The invention provides a projection display device capable of appropriate light control depending on the kind of the image, the ambient brightness and so on, a method for driving the same, and an illuminator used in the same. The light flux of illumination can be adjusted on the basis of image information. The allowable light control range (dimming control) can be optimally set depending on the information (usage information) on the kind of viewed content, the brightness of viewing environment, the gain of a screen and the like.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an illuminator, a projection displaydevice having the same, and a method for driving the same. Moreparticularly, the invention relates to a projection display devicehaving excellent image expression and an illuminator used therein.

2. Related Art

Information technology devices have greatly been developed, thusincreasing a demand for display devices with high resolution, low powerconsumption, and low profile, and thus advancing research anddevelopment. Among them, liquid crystal displays are expected to be ableto change optical characteristics by electrically controlling thealignment of liquid crystal molecules to thereby match theabove-described needs. A known example of such liquid crystal displaysis a projection display device (liquid crystal projector) that projectsan image emitted from an optical system using a liquid-crystal lightvalve, on an enlarged scale, onto a screen through a projector lens.

The projection display device uses a liquid-crystal light valve as lightmodulation device. In addition, a digital micro mirror device (DMD) isalso in practical use as light modulator. The conventional projectiondisplay devices of this type have the following problems:

Sufficient contrast cannot be provided because of light leakage andstray light occurring in various optical elements that construct theoptical system, thus having a narrow display luminous range (dynamicrange), and thus being inferior to existing TV monitors using a cathoderay tube (hereinafter, referred to as a CRT) in image quality andimpression.

Even when an increase in image quality is intended by variousimage-signal processings, sufficient effects cannot be given because ofthe fixed dynamic range.

The solution to the problems of the projection display devices, briefly,the method for expanding the dynamic range, includes changing theintensity of light incident on the light modulation device (light valve)depending on the image signal. To that end, it is known in the art toprovide light flux adjusting device (light control device) in front of alight source. See, for example, JP-A-05-066501.

As described above, the adaptive light control in which the light fluxof illumination and the brightness of the display image are varieddepending on the contents (for example, brightness) of the display imageis effective in increasing the contrast or tone reproduction. However,it tends to cause deterioration of gradations and insufficientbrightness in highlight areas. Therefore, it is effective for imageshaving dark images as moving pictures, while it may not be effective forones having light images as sportscasting, probably acting negatively bythe occurrence of flickering.

The display characteristic of shadow areas is not so increased when theprojection image is viewed in light environment that the contrast may bedecreased because of insufficient brightness.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a projection display devicecapable of appropriate light control depending on the kind of the imageand the ambient brightness, or the like, a method for driving the same,and an illuminator used therein.

As described above, the adaptive light control is very effective inincreasing image expression, however, the light control is alwaysperformed under the same condition without considering the device usagesituation. Thus the light flux of illumination is excessively adjustedin some cases to apply a stress to viewers. Accordingly, the inventionadopts the information on usage situation (usage information) as alight-control parameter and controls the light flux of a light source onthe basis of the usage information.

In order to achieve the above objects, the illuminator according to theinvention which is used to illuminate a light modulation device of aprojection display device can include a light source, and a lightcontrol device that adjusts the light flux of the light source on thebasis of image information and usage information.

The usage information can include, for example, the kind of an image,the brightness of viewing environment, screen gain, and userpreferences. In this specification, the light flux of a light source isthe ratio of the outputted light flux to a maximum light flux that thedisplay device is able to irradiate. Similarly, an dimming amount is andimming ratio relative to the maximum light flux.

The light control based on the usage information allows flexible lightcontrol in touch with reality. For example, when the usage informationrelates to the brightness of viewing environment, the dimming amount ofthe light source can be reduced when the ambient is bright, while thedimming amount is increased when the ambient is dark. Thus, the problemof insufficient brightness caused by excessive light control can besolved.

A method of actively varying the dimming amount depending on the usageinformation may be adopted as specific control method. A method oflimiting the range in which dimming is allowed on the basis of the usageinformation may be adopted to facilitate light control. Morespecifically, the light control device may include light flux settingdevice for setting the light flux of the light source on the basis ofimage information and a dimming-range setting device for setting dimmingrange in which dimming is allowed on the basis of the usage information.The light control device adjusts the light flux of the light source onthe basis of the set light flux and inhibits dimming exceeding thedimming range (briefly, the light control device adjusts the light fluxwithin the dimming range).

With this arrangement, the dynamic range of the projection image can beexpanded by appropriate adjustment of the light flux of illuminationdepending on the image information. Also the problem of insufficientbrightness and the like can be solved without quality loss in imageexpression by limiting the dimming range of the light flux within afixed range depending on the kind of the image and viewing environment.For example, when the viewing environment is bright or the image itselfis bright and so light control works negatively, the dimming range ismade narrower than normal (that is, the maximum allowable dimming amountis reduced), so that the problem of the insufficient brightness can besolved.

When the dimming amount of the set light flux exceeds the dimming range,the light flux control may be stopped. Alternatively, the light flux ofthe light source may be adjusted depending on the dimming amount withinthe dimming range.

The usage information may be inputted manually by a user or,alternatively, may be measured automatically by a sensor of the device.

The example of automatically measuring the usage information can includethe structure in which the device has brightness measuring device formeasuring the brightness of the projection-image viewing environment(for example, the brightness around the device and the brightness aroundthe screen) and in which the dimming-range setting device sets the rangeon the basis of the brightness of the viewing environment. With thisarrangement, for example, reducing the dimming range as the viewingenvironment becomes brighter (that is, the maximum allowable dimmingamount is reduced) allows the entire image to be displayed more brightlythan usual when the ambient is bright. Accordingly, high-qualityprojection images can be enjoyed without the feeling of insufficientbrightness even in a bright room.

Another example is a structure in which the device has gain measuringmeans for measuring the gain of a projected-image display screen. Thedimming-range setting device sets the dimming range on the basis of thegain. The tone reproduction effect by the light control increases as thecontrast of the projection image increases. The contrast of the imagevaries depending on not only the performance of the display deviceitself but also on the projection screen. For example, with large screengain, the contrast of the image is increased, while with small gain, thecontrast is decreased. Accordingly, as in this arrangement, by adjustingthe light control amount depending on the screen gain, theconstant-quality projection images are provided constantly irrespectiveof the difference of the screens.

A projection display device according to the invention can include theilluminator, a light modulation device for modulating the light emittedfrom the illuminator to form image light, and a projection device forprojecting the image light. With the arrangement, constant-qualityimages can be constantly provided to a user by proper light controldepending on the usage situation.

Preferably, the projection display device further can include animage-signal expanding device for expanding the image signal on thebasis of the dimming amount of the light source as the driving device.With the arrangement, first, an dimming range in which dimming isallowed is set by the dimming-range setting device on the basis of useinformation. The light flux of the light source is adjusted within thedimming range on the basis of the image signals per unit time (during aperiod), the image signals are expanded on the basis of the dimmingamount of the light source, and the expanded image signals are sent tothe light modulation means; thus, an image is formed. Accordingly, thedynamic range of the projection display device can be expanded torealize a projection display device with high image expression andadaptability to usage environment.

In this case, preferably, when the dimming amount of the light fluxwhich is set by the light flux setting device is within the dimmingrange, the image-signal expanding device expands the image signal by anexpansion amount that is the complement of the light flux, whereas whenthe dimming amount of the set light flux is out of the dimming range,the image-signal expanding device expands the image signal by anexpansion amount larger than the reciprocal.

With the conventional light control in which the dimming amount is notlimited, the light flux of the light source is always adjusted with aset dimming amount. Therefore, the product of the expansion amount andthe light flux needs to be set to one or less to make the expanded imagesignal equal to or less than the maximum displayable gray level. On theother hand, with the light control in which the dimming is limited to belower than a certain value, as in the invention, the signal that has themaximum gray level of the image signals is not expanded to the maximumdisplayable gray level even by the conventional expanding process basedon the limited dimming amount (the process in which the product of theexpansion amount and the light flux becomes one or less). In otherwords, when the set dimming amount comes out of the dimming range, thereis some margin of gray levels in a high gray-level region even ifexpanding process is performed under the condition that the product ofthe expansion amount and the light flux is one, so that sufficient tonereproduction is not obtained. Accordingly, setting the product of theexpansion amount and the light flux higher than one with the dimminglimited, as in this arrangement, a decrease in tone reproduction can beprevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numerals reference like elements, and wherein:

FIG. 1 is a schematic diagram of a projection display device accordingto a first embodiment of the invention;

FIG. 2 is an exemplary block diagram of a configuration of a controllerof the projection display device of the same;

FIG. 3 is an exemplary block diagram of an essential part of thecontroller of the same;

FIG. 4 is an explanatory diagram of a first method for determining alight-source control signal based on a image signal in the projectiondisplay device of the same;

FIG. 5 is an explanatory diagram of a second method of the same;

FIG. 6 is an explanatory diagram of a third method of the same;

FIG. 7 is an explanatory diagram of a method for determining an imagecontrol signal based on a light-source control signal in the projectiondisplay device of the same;

FIG. 8 is an explanatory diagram of a method for determining an imagecontrol signal of the same;

FIG. 9 is an explanatory diagram of a method for determining an imagecontrol signal of the same;

FIG. 10 is an exemplary block diagram of a controller of a projectiondisplay device according to a second embodiment of the invention;

FIG. 11 is an exemplary block diagram of an essential part of thecontroller of the same;

FIG. 12 is an explanatory diagram of a method for determining a maximumdimming amount based on ambient-light flux signal in the projectiondisplay device of the same;

FIG. 13 is an exemplary block diagram of a controller of a projectiondisplay device according to a third embodiment of the invention; and

FIG. 14 is an exemplary block diagram of an essential part of thecontroller of the same.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 to 8, a projection display device according to afirst embodiment of the invention will now be described.

The projection display device of the embodiment is athree-light-valve-liquid-crystal projection display device including atransmissive liquid-crystal light valve for each of different colors ofred (R), green (G), and blue (B).

FIG. 1 shows the schematic arrangement of the projection display device,wherein reference numerals 10R, 10G, and 10B denote three light sourcesconstructing an illuminator of the invention, respectively, referencenumerals 20R, 20G, and 20B denote liquid-crystal light valves (lightmodulation device), numeral 30 denotes a cross-dichroic prism, numeral40 denotes a projector lens (projection device), and numeral 41 denotesa screen.

The light sources 10R, 10G, and 10B are color light sources capable ofemitting red light, green light, and blue light, respectively, whereinthe respective light sources 10 (10R, 10G, 10B) includes a light emitter11, such as a light-emitting diode (LED), an organic electroluminescenceelement (organic EL element), and an inorganic electroluminescenceelement (inorganic EL element) and a reflector 12 for reflecting thelight from the light emitter 11. The light valves 20R, 20G, and 20B arearranged to correspond to the light sources 10R, 10G, and 10B,respectively, being capable of light modulation for each light source.

The cross-dichroic prism 30 has a structure in which four rectangularprisms are bonded together, having a light reflective film (not shown)formed of a dielectric multilayer film in cross shape on the bondedsurfaces 30 a and 30 b. More specifically, the bonded surface 30 a has alight reflective film that reflects red image light formed by the lightmodulator 20R and transmits green and blue image lights formed by thelight modulators 20G and 20B, respectively. On the other hand, thebonded surface 30 b has a light reflective film that reflects blue imagelight formed by the light modulator 20B and transmits red and greenimage lights formed by the light modulators 20R and 20G, respectively.With the light reflective films, the respective color image light raysformed by the liquid-crystal light valves 20R to 20B are combined toform light representing a color image. The combined light is projectedonto the screen 41 through the projector lens 40 which is a projectionoptical system to display an enlarged image.

A method for driving the projection display device of the embodimentwill now be described.

FIG. 2 is an exemplary block diagram showing the configuration of acontroller 60 of the projection display device of the embodiment. Theembodiment is constructed to adjust the light flux of the light sourceon the basis of both image information and information (usageinformation) on the usage situation of the device. Accordingly, theprojection display device of the embodiment includes a signal input unit101 for inputting a image signal as an external input unit and acontroller 102 (usage-information input device) for setting dimmingrange of the light source depending on the kind of a viewed image,ambient brightness, user preferences.

With the controller 102, the dimming range is designated on the basisof, for example, the maximum allowable dimming amount (the maximumdimming amount) R_(m). The method of designation may be either a methodin which a user directly inputs the maximum dimming amount R_(m)numerically or a method in which a user selects it from the dimmingrange displayed on a menu screen. The latter example includes astructure in which the menu includes “normal,” “dynamic,” “sports,” and“no light control” and their maximum dimming amounts are 50%, 75%, 25%,and 0%, respectively. When the maximum dimming amount R_(m) isdesignated, the dimming amount of the dimming range is set equal to orsmaller than the maximum dimming amount R_(m) (or, the dimming amount iswithin the range of 0 to R_(m)). The information on the dimming range isinputted as a user control signal to the controller 60.

The controller 60 can include an image analyzer (light control means) 61for setting the light flux T of each of the light sources 10R, 10G, and10B and the expansion amount P₀ of the respective color image signals onthe basis of the image signal and the user control signal, alight-source control driver 64 for driving the light sources 10R, 10G,and 10B on the basis of the light flux T set by the image analyzer 61,an image processor (image signal expansion device) 62 for expanding therespective color image signals on the basis of the set expansion amountP₀, and a panel driver 63 for sending the expanded color image signalsto the red-light liquid-crystal light valve 30R (R-panel in FIG. 5), thegreen-light liquid-crystal light valve 30G (G-panel in the same), andthe blue-light liquid-crystal light valve 30B (B-panel in the same).

Referring to FIG. 3, the image analyzer 61 includes a histogram makingsection 61 a, a histogram analyzer 61 b, an dimming-range settingsection 61 c, and a light flux setting section 61 d. In the imageanalyzer 61, when image signals are inputted from the signal input unit101, the histogram-making section 61 a makes a pixel data distribution(histogram) for each gray level, contained in the signals per unit time(for one frame). The histogram analyzer 61 b determines the brightnessof the image on the basis of the histogram to set the light flux of thelight sources 10R, 10G, and 10B. Briefly, the histogram analyzer 61 bfunctions as a light flux setting device of the invention.

A method for measuring the brightness using the histogram will now bedescribed. The method includes, for example, the following threemethods:

(a) A method of measuring the brightest gray level of the pixel datacontained in the target frame as the brightness of the image.

Suppose an image signal containing 256 steps of gray levels from 0 to255. For an arbitrary one frame that constructs continuous images,assume that a pixel data distribution (histogram) contained in the framefor each gray level is obtained as shown in FIG. 4. In this case, thebrightest gray level in the histogram is 190; thus, the 190 levels ofgray are the brightness of the image. The method is one in which thebrightness can be expressed most faithfully for the inputted imagesignals.

(b) A method of measuring the gray level of a certain ratio (forexample, 10 percent of a image) to the brightest level in thedistribution (histogram) for each gray level contained in a targetframe, as the brightness of the image.

When the image-signal distribution is as shown in FIG. 5,10-percent-area from the brightest level is taken in the histogram.Assuming that the gray level of the area corresponding to 10 percent is230, the 230 levels of gray are determined as a light-control signal.When there is a sharp peak near level 255, as in the histogram of FIG.5, the level 255 is determined as a light-control signal by theabove-described method (a). The sharp peak, however, does not make senseas information on the entire screen. On the other hand, the method ofdetermining the 230 levels of gray as the brightness of the image can bereferred to as a method of measuring the brightness with a significantarea in the entire screen as information. The ratio may be varied in therange on the order of 0.1 to 50 percent.

(c) A method of dividing the image into a plurality of areas andobtaining the mean value of the gray levels of the pixels contained ineach area, of which the maximum one is taken as the brightness of theimage.

Referring to FIG. 6, for example, the screen is divided into m×n areas,and the mean value of the brightness (the number of gray levels) foreach of the blocks A₁₁ to A_(mn) is calculated, of which the maximum oneis taken as the brightness of the image. The number of divisions of thescreen is desirably on the order of 6 to 200. The method is capable ofcontrolling the brightness without loss of the atmosphere of the entirescreen.

With the above methods (a) to (c), the determination of the brightnessof the image may be made for a specific part, such as the center of thedisplay region, instead of being made for the entire display region.This allows the control in which the brightness is determined from thepart to which a viewer's attention is being given.

Suppose that the number of gray levels 190 is measured as the brightnessof the image in this way. Letting the light flux (the maximum lightflux) of the maximum brightness (for example, 255 levels of gray) be 100percent, 190/255=75% is temporarily set as the light flux T₀ of thelight source when the display gamma characteristic is 1.0.

The dimming-range setting section (dimming-range setting means) 61 csets a range in which dimming is allowed (dimming range) on the basis ofthe user control signal.

The set light flux T₀ and the dimming range are inputted to the lightflux setting section 61 d, where a light flux T which is used for actuallight-source control is determined. More specifically, when the dimmingamount of the temporarily set light flux T₀ is within the dimming range(that is, equal to or lower than the maximum dimming amount R_(m)), thelight flux setting section 61 d uses the temporarily set light flux T₀as the actual light flux T. On the other hand, when the dimming amountof the temporarily set light flux T₀ is out of the dimming range (thatis, larger than the maximum dimming amount R_(m)), the light fluxsetting section 61 d sets the actual light flux T to a light flux thatis obtained by attenuating light from the maximum light flux by andimming amount (dimming amount of 0 to R_(m)) within the dimming range.In this embodiment, for example, the light flux that is obtained byattenuating light from the maximum light flux by the maximum dimmingamount R_(m) is set as the actual light flux T. The light flux T whichis set in this way is outputted as a light-source control signal to alight-source control driver 64. The light-source control driver 64controls the light flux and the period of light emission of the lightsources 10R to 10B in accordance with the light-source control signal tothereby adjust the light flux.

The light flux setting section 61 d can also set the expansion amount P₀of the image signal depending on the actual light flux T. Morespecifically, when the dimming amount of the temporarily set light fluxT₀ is within the dimming range, the reciprocal (1/T) of the light flux Tis set as the expansion amount P₀. On the other hand, when the dimmingamount of the temporarily set light flux T₀ is out of the dimming range,the expansion amount P₀ is set larger than the reciprocal (1/T) of thelight flux T. The expansion amount P₀ which is set in this way isoutputted as an image control signal to the image processor 62.

FIGS. 7 and 8 show examples of expansion processing in the case in whichthe maximum dimming amount R_(m) is set to 25 percent (i.e., the dimmingrange is set to a range where the dimming amount is from 0 to 25percent) and the brightness of the image is obtained as the brightestgray level in the histogram. In FIGS. 7 and 8, the light flux and theexpansion amount in the case where the light of the light source isattenuated by the maximum dimming amount R_(m) are indicated by T_(m)and P_(m), respectively.

Suppose that the histogram of the pixel data in one frame plottedagainst the number of gray levels is as in FIG. 7( a). The brightestgray level in the histogram is 217, thus, the brightness of the image isthe 217 levels, in which case the temporarily set light flux T₀ is217/255=85%. Since the dimming amount of the temporarily set light fluxT₀ is within the dimming range, the light flux T₀ is used for the lightflux T outputted as a light-source control signal. The expansion amountP₀ is set to 1/T₀=1.18 using the light flux T₀. The image signals of 0to 217 levels of gray are expanded to 0 to 255 levels of gray by theexpansion processing by the image processor 62 (refer to FIG. 7( b)).

Suppose that the histogram is as in FIG. 8( a). The brightest gray levelin the histogram is 128, thus, the brightness of the image is the 128level, in which case the temporarily set light flux T₀ is 128/255=50%.

Since the dimming amount of the light flux T₀ is out of the dimmingrange, the light flux T outputted as the light-source control signal isa light flux obtained by attenuating light from the maximum light fluxby the maximum dimming amount R_(m). The expansion amount P₀ is set to1/(1−R_(m))=P_(m)=1.33 using the maximum dimming amount R_(m) forexample. The image signals of 0 to 128 level of gray are expanded to 0to 171 levels of gray by the expansion processing by the image processor62 (refer to FIG. 8( b)).

When the expansion amount is set as above, however, the number of graylevels after the expansion, even of pixel data in which the gray levelsis the maximum in the image signals, becomes smaller than the maximumdisplayable gray level (255 level). In other words, according to thissetting method, there occur remaining gray levels in a high gray-levelregion, not providing sufficient tone reproduction. T₀ solve theproblem, as shown in FIG. 9( a), the expansion amount may be set to avalue P′ larger than P_(m) and smaller than P₀. FIG. 9( a) shows anexample of setting the expansion amount P′ at 1.66 while the light fluxT is maintained. In this case, since the image signals from 0 to 128levels of gray are expanded to 0 to 213 levels of gray by the expansionprocessing by the image processor 62, the problem of the remaining graylevels is relieved (refer to FIG. 9( b)). In this case, the dimmingamount remains R_(m). Consequently, the entire image becomes bright,thereby providing a display more suitable for usage situation.

As described above, this embodiment incorporates the information on thedevice usage situation for light control. Accordingly, the dimmingamount of the light source can be adjusted optimally depending on thekind of the images and the brightness of the viewing environment,allowing flexible light control in touch with reality. For example, theembodiment limits the dimming amount of the light source on the basis ofthe usage information. Thus, the dynamic range of the projection imagecan be expanded by appropriate adjustment of the light flux ofillumination depending on the image information. Also the problem ofinsufficient brightness and the like can be solved without quality lossin image expression by limiting the dimming range of light flux within afixed range depending on the kind of the image and the viewingenvironment.

The method for light control in view of the device usage situation caninclude a method of actively varying the dimming amount of the lightsource depending on the usage information, in addition to the method ofthe embodiment.

The device usage situation, however, does not vary greatly during imagedisplay. Accordingly, also the static control system in which thedimming amount of the light source is limited on the basis of the usageinformation, as in this embodiment, offers the above-described effectssufficiently, and being advantageous in cost because of easy control.

Referring now to FIGS. 10 and 11, a projection display device accordingto a second embodiment of the invention will be described. In thisembodiment, the same components as those of the first embodiment aregiven the same reference numerals and their description will be omitted.

FIG. 10 is an exemplary block diagram of the arrangement of a controller70 of the projection display device according to this embodiment. Theembodiment is constructed to measure the ambient brightness as usageinformation and to automatically set an dimming range depending on thebrightness. Specifically, the embodiment can include a photosensor(usage-information input means) 103 for measuring the brightness ofviewing environment, in addition to the signal input unit 101 forinputting a image signal as an external input unit. The environmentalbrightness measured by the photosensor 103 may be either the brightnessin the vicinity of the projection display device or the brightness inthe vicinity of a screen. The information of the brightness of theviewing environment is inputted to the controller 70 as an ambient-lightflux signal.

The controller 70 can include an image analyzer (light control means) 71for setting the light flux T of the light sources 10R to 10B and theexpansion amounts P₀ of the color image signals on the basis of theimage signals and the ambient-light flux signal, a light-source controldriver 74 for driving the light sources 10R to 10B on the basis of thelight flux adjusted amount set by the image analyzer 71, an imageprocessor (image-signal expanding means) 72 for expanding the colorimage signals on the basis of the set expansion amount P₀, and a paneldriver 73 for sending the expanded color image signals to the red-lightliquid-crystal light valve 30R (the R-panel in FIG. 5), the green-lightliquid-crystal light valve 30G (the G-panel in the same), and theblue-light liquid-crystal light valve 30B (the B-panel in the same),respectively.

Referring now to FIG. 11, the image analyzer 71 can include a histogramforming section 71 a, a histogram analyzer 71 b, a brightness measuringsection 71 c, and a light flux setting section 71 d.

In the image analyzer 71, when image signals are inputted from thesignal input unit 101, the histogram forming section 71 a forms a pixeldata distribution (histogram) for each gray level, contained in thesignals per unit time (for one frame). The histogram analyzer 71 bmeasures the brightness of the image on the basis of the histogram toset the light flux of the light sources 10R to 10B. Briefly, thehistogram analyzer 71 b functions as light flux setting means of theinvention. The method of measuring the brightness using the histogramand the method of setting the light flux T₀ by the histogram analyzer 71b may be the same as those of the first embodiment.

The brightness measuring section 71 c sets a range in which dimming isallowed (dimming range) on the basis of an ambient-light flux signalwith reference to a look-up table (LUT). The LUT is a control table thatspecifies the relationship between the brightness of viewing environment(ambient light flux) and the maximum allowable dimming amount (themaximum dimming amount) R_(m), in which the dimming range is set as arange where the dimming amount is equal to or lower than the maximumdimming amount R_(m). In the LUT, as shown in FIG. 12, the higher theambient light flux is, the lower the maximum dimming amount R_(m) isspecified, when the viewing environment is bright, the dimming range isnarrowed. In other words, the brightness measuring section 71 cfunctions as a brightness measuring device and a dimming-range settingdevice of the invention.

The set light flux T₀ and the dimming range are inputted to the lightflux setting section 71 d, where the light flux T which is used foractual light-source control and the expansion amount P₀ of the imagesignal are determined. The method of setting the light flux T and theexpansion amount P₀ may be the same as that of the first embodiment.

In this embodiment, accordingly, when the ambient light flux is high, anentire image is displayed more brightly than usual, allowinghigh-quality projection images to be enjoyed without the feeling ofinsufficient brightness even in a bright room.

Referring now to FIGS. 13 and 14, a projection display device accordingto a third embodiment of the invention will be described. In thisembodiment, the same components as those of the first embodiment aregiven the same reference numerals and their description will be omitted.

FIG. 13 is an exemplary block diagram of the arrangement of a controller80 of the projection display device according to this embodiment. Theembodiment is constructed to measure screen gain as ambient light fluxand to automatically set an dimming range depending on the screen gain.Specifically, the embodiment can include a photosensor(usage-information input means) 104 for measuring the reflected lightflux from the screen, in addition to the signal input unit 101 forinputting an image signal as an external input unit. For example, theentire white image is displayed on the screen before image display andthe reflected light flux of the image is measured by the photosensor104. The information on the reflected light flux from the screen,measured by the photosensor 104, is inputted to the controller 80 as areflected-light flux signal.

The controller 80 includes an image analyzer (light control means) 81for setting the light flux T of the light sources 10R to 10B and theexpansion amounts P₀ of the color image signals on the basis of theimage signals and the reflected-light flux signal, a light-sourcecontrol driver 84 for driving the light sources 10R to 10B on the basisof the light flux adjusted amount set by the image analyzer 81, an imageprocessor (image-signal expanding means) 82 for expanding the colorimage signals on the basis of the set expansion amount P₀, and a paneldriver 83 for sending the expanded color image signals to the red-lightliquid-crystal light valve 30R (the R-panel in FIG. 5), the green-lightliquid-crystal light valve 30G (the G-panel in the same), and theblue-light liquid-crystal light valve 30B (the B-panel in the same),respectively.

Referring now to FIG. 14, the image analyzer 81 can include a histogramforming section 81 a, a histogram analyzer 81 b, a gain measuringsection 81 c, and a light flux setting section 81 d.

In the image analyzer 81, when image signals are inputted from thesignal input unit 101, the histogram forming section 81 a forms a pixeldata distribution (histogram) for each gray level, contained in thesignals per unit time (for one frame). The histogram analyzer 81 bmeasures the brightness of the image on the basis of the histogram toset the light flux of the light sources 10R to 10B. Briefly, thehistogram analyzer 81 b functions as light flux setting means of theinvention. The method of measuring the brightness using the histogramand the method of setting the light flux T₀ by the histogram analyzer 81b may be the same as those of the first embodiment.

The gain measuring section 81 c measures the screen gain in accordancewith the reflected-light flux signal and sets a range in which dimmingis allowed (dimming range) on the basis of the screen gain withreference to a look-up table (LUT). The LUT is a control table thatspecifies the relationship between the screen gain and the maximumallowable dimming amount (the maximum dimming amount) R_(m). In the LUT,the larger screen gain is, the larger the maximum dimming amount R_(m)is specified. The dimming range is narrowed in the state in which thecontrast is displayed low. The dimming range is set as a range where thedimming amount is equal to or smaller than the maximum dimming amountR_(m). In other words, the gain measuring section 81 c functions as again measuring device and a dimming-range setting device of theinvention.

The set light flux T₀ and the dimming range are inputted to the lightflux setting section 81 d, where the light flux T which is used foractual light-source control and the expansion amount P₀ of the imagesignal are determined. The method of setting the light flux T and theexpansion amount P₀ may be the same as that of the first embodiment.

In this embodiment, accordingly, the larger the screen gain is, thelarger the dimming amount is, thus preventing a decrease in imagequality due to the difference of screens. In other words, the higher thecontrast of the projection image is, the larger the tone reproductioneffects by light control are. The contrast of the image varies dependingon not only the performance of the display device itself but also on theprojection screen. For example, with large screen gain, the contrast ofthe image is high, while with small gain, the contrast is low.Accordingly, by controlling the light control depending on the screengain, as in this arrangement, uniform-quality projection images areprovided constantly irrespective of the difference of the screens.

It should be understood that the technical scope of the invention is notlimited to that of the above embodiments, and various modifications maybe made without departing from the spirit and scope of the invention.

For example, the embodiments include three color light sources made ofLEDs or the like and control respective light intensities and periods oflight emission to thereby adjust the light flux. Instead, a lightcontrol device, which is constructed of a douser, a liquid crystaldevice and so on, may be provided on the optical axis of the lightemitted from each light source, with which the light flux of theemission light from the light source may be reduced to adjust the lightflux. Specifically, the light flux of emission light can be adjusted byadjusting the light transmission of the liquid crystal device, theperiod of light transmission of the liquid crystal device, the movementof the douser, and the period of the movement of the douser.

The arrangement of the projection display device of FIG. 1 is merely anexample and other arrangements may be adopted. More specifically, theprojection display device may include a light source, a color separationdevice for separating the light emitted from the light source into aplurality of color lights, a light modulation device providedcorresponding to the divided colors, a light combining device forcombining the color lights modulated by the light modulation device, anda projection device for projecting the light combined by the colorcombining device. In this case, the light flux is adjusted by directlycontrolling the light source or, alternatively, by providing a lightcontrol device between the light source and the light modulation deviceor on the side of the light emission of the light modulation device.

Although the embodiments have been described taking a projection displaydevice using a liquid crystal light valve as a light modulation deviceas an example, it should be understood that the invention may be appliedto a projection display device using a DMD as a light modulation device.

While this invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart. Accordingly, preferred embodiments of the invention as set forthherein are intended to be illustrative, not limiting. There are changesthat may be made without departing from the spirit and scope of theinvention.

1. An illuminator used to illuminate a light modulation device of aprojection display device, comprising: a light source; a light controldevice that adjusts an amount of a light flux of the light source on thebasis of image information and usage information, the light controldevice including a light flux setting device that sets the amount oflight flux of the light source on the basis of image information and adimming-range setting device that sets a dimming range in which dimmingis allowed on the basis of the usage information; and an image-signalexpanding device that expands an image signal on the basis of a dimmingamount of the light source, wherein the light control device adjusts theamount of light flux of the light source on the basis of the amount oflight flux set by the light flux setting device within the dimmingrange, and the light flux setting device temporarily sets a temporaryamount of the light flux, when a dimming amount of the temporary amountof the light flux is within the dimming range, the image-signalexpanding device expands the image signal by an expansion coefficientthat is a reciprocal of the temporary amount of light flux, whereas whenthe dimming amount of the temporary amount of light flux is out of thedimming range, the image-signal expanding device expands the imagesignal by an expansion amount larger than the reciprocal.
 2. Theilluminator according to claim 1, the usage information being manuallyset.
 3. The illuminator according to claim 1, further comprising: abrightness measuring device that measures a brightness of a usageenvironment, the dimming-range setting device setting the dimming rangeon the basis of the brightness of the usage environment.
 4. Theilluminator according to claim 1, further comprising: a gain measuringdevice that measures a gain of a screen, the dimming-range settingdevice setting the dimming range on the basis of the gain.
 5. Aprojection display device, comprising: the illuminator according toclaim 1; a light modulation device that modulates light emitted from theilluminator to form an image; and a projection device that projects theimage.
 6. The projection display device according to claim 5, the usageinformation being manually set.
 7. The projection display deviceaccording to claim 5, further comprising a brightness measuring devicethat measures a brightness of a usage environment, the dimming-rangesetting device setting the dimming-irate range on the basis of thebrightness of the usage environment.
 8. The projection display deviceaccording to claim 5, further comprising a gain measuring device thatmeasures a gain of a screen, the dimming-range setting device settingthe dimming-irate range on the basis of the gain.
 9. A method fordriving the projection display device including: a light source; a lightcontrol device that adjusts an amount of a light flux of the lightsource on the basis of image information and usage information; and alight modulation device that modulates light emitted from the lightsource to form an image, the method comprising: setting a dimming rangein which dimming is allowed on the basis of the usage information;adjusting the amount of the light flux of the light source within therange on the basis of image signals in unit time (during a period);expanding the image signals on the basis of a dimming amount of thelight source and transmitting the expanded image signals to the lightmodulation device to form an image; temporarily setting a temporaryamount of the light flux based on the image information; expanding theimage signal by an expansion coefficient that is a reciprocal of thetemporary amount of light flux, when the dimming amount of the temporaryamount of light flux is within the dimming range; and expanding theimage signal by an expansion amount larger than the reciprocal, when thedimming amount of the temporary amount of light flux is out of thedimming range.